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Ohm’s Law
Electronic Training Course
Slide# 1
Ohm’s Law
Review of Current, Voltage and Resistance
An electric current is the flow of electrons through a conductor and is measured in
Amperes commonly called Amps. Current always flows through a conductor from
the negative side of the battery to the positive side of the battery.
The letter “I” is used to represent current.
Slide# 2
Ohm’s Law
Review of Current, Voltage and Resistance
Voltage is the force or electric pressure that causes current to flow. Voltage is
created by the accumulation of negative and positive charges on the poles of a
battery or electric generator. Voltage is measured in volts.
The letter “V” (and sometimes “E”) is used to represent voltage.
Slide# 3
Ohm’s Law
Review of Current, Voltage and Resistance
Resistance is the opposition to current flow or the resistance that a material
presents to the flow of electric current through it. Good conductors such as gold,
copper, and silver have low resistance and good insulators such as porcelain, glass,
and plastic have high resistance. Resistance is measured in ohms (Ω).
The letter “R” is used to represent resistance.
Slide# 4
Ohm’s Law
Current, voltage, and resistance are three elements or parameters found in every
electric or electronic circuit no matter how simple or complex the circuit is. In the
simple circuit shown above, these three elements are present. The battery
supplies the voltage (V), the resistor and the wires have resistance (R), and there
is a current (I) that flows through the circuit as a result of voltage from the
battery.
Slide# 5
Ohm’s Law
Ohm's Law establishes the relationship between voltage, current and resistance in
a circuit. This law states that the amount of current flowing in a circuit depends
upon the amount of voltage in the circuit and the amount of resistance in the
circuit.
Now let's breakdown Ohm's Law.
Slide# 6
Ohm’s Law
Voltage Effects
First we are going to find out how the amount of voltage affects the
current flowing in a circuit, or in other words, what happens to the
current (I) when we increase the voltage (V)? Does the current
increase when the voltage increases? Or Does the current decrease
when the voltage increases?
To find out, we will connect four batteries with different voltages,
one by one, to points A and B of the circuit in the next slide and we
will observe how this affects the amount of current flowing in the
circuit. The light bulb in the circuit will help us to identify the level of
current (the larger the current the brighter the bulb will glow, the
smaller the current the dimmer the bulb).
Slide# 7
Ohm’s Law
Figure B shows the circuit of Figure A with a 1.5 volt battery in place. Notice the
small current that flows in the circuit that can barely light the filament of the bulb.
Figure C shows the same circuit as Figure A but with a 3 volt battery connected to
it. Notice that the current is larger than the one produced with the 1.5 volt
battery. Also notice the intensity of the light.
Slide# 8
Ohm’s Law
Figure D shows the same circuit but with a 6 volt battery. Notice that the current
is larger and the lamp glows even brighter. Figure E shows the same circuit with a
12 volt battery. Notice that the current is larger and the light is even brighter still.
Therefore, from what you have observed in Figures B - E: What happens to the
current when we increase the voltage in a circuit?
Slide# 9
Ohm’s Law
As we have found, the current increases when the voltage increases and the
current decreases when the voltage decreases. Therefore, we can say that the
current in the circuit is directly proportional to the voltage in the circuit.
A larger voltage will produce a larger current, a smaller voltage will produce a
smaller current.
Slide# 10
Ohm’s Law
Resistance Effects
Now let's find out what happens to the amount of the current
flowing in a circuit when we increase the amount of resistance.
To do this we will connect four resistors of different values: 10, 50,
100, and 1000 ohms between points C and D in the circuit. On the
next slide one let's observe what happens to the current as we do
this.
Slide# 11
Ohm’s Law
Figure B shows the circuit of Figure A with a 10Ω resistor connected to it. Notice
that a large current flows in the circuit and that the light bulb is very bright.
Figure C shows the same circuit but with a 50Ω resistor. Notice that the current
and the brightness of the light bulb have decreased.
Slide# 12
Ohm’s Law
Figure D shows the same circuit with a 100Ω resistor. Notice that the current is
smaller and the light is not as bright. Figure E shows the same circuit with a
1000Ω resistor connected to it. Notice that the current is very small and that the
light is nearly off.
Therefore, from what you have seen in Figures B to E: What happens to the
current in a circuit when we increase the value of the resistance?
Slide# 13
Ohm’s Law
As we have found, the current decreases when the resistance increases. This
makes sense because more resistance means more opposition to current flow
which reduces the current flowing in a circuit. Therefore we can say that the
amount of current in a circuit is inversely proportional to the amount of
resistance, which means, the greater the resistance, the smaller the current, and
the smaller the resistance, the greater the current. Now we can say that we have
proven Ohm's Law.
Slide# 14
Ohm’s Law
Basically, Ohm's Law states that the current that flows in a circuit is directly
proportional to the voltage and inversely proportional to the resistance. Which
means, as you know, that when the voltage increases the current increases and
when the resistance increases the current decreases.
Slide# 15
Ohm’s Law
The mathematical formula for Ohm's Law is shown here. We can use this formula
to calculate the value of the current flowing in a circuit when we know the voltage
of the battery and the amount of the resistance. From the basic formula of Ohm's
Law the other two formulas can be derived: V = I x R and R = V/I.
Slide# 16
Ohm’s Law
We can use the V = I x R formula to calculate an unknown voltage when we know
the current and the resistance. We can use the other formula R = V/I to calculate
an unknown resistance when we know the values of the voltage and the current in
a circuit.
There is an easy way to memorize the three formulas of Ohm's Law by memorizing
the Ohm's Law Circle. Using this circle, the three formulas of Ohm's Law can be
obtained by covering the value that you want to calculate.
Slide# 17
Ohm’s Law
For example, to obtain the formula for voltage (V), cover the V in the Ohm's Law
circle and what's left is I x R. The vertical line separating the I and R should be
interpreted as multiplication. If you want the formula for current, cover the I and
what's left is V/R. The same technique can be followed for the formula to
calculate resistance (R).
Slide# 18
Ohm’s Law
Here we see three examples of how the formulas of Ohm's Law are used to
calculate current, voltage and resistance in a circuit.
In the circuit on the left we have connected a 12 volt battery and a 10Ω resistor
and we want to know the value of the current that will flow through this circuit.
We can easily calculate the value of the current using Ohm's Law as shown.
Slide# 19
Ohm’s Law
In the circuit shown in the middle we know the value of the resistor and the value
of the current but we do not know the voltage of the battery. We can easily
calculate the voltage of the battery by again using Ohm's Law as shown in the
figure.
Slide# 20
Ohm’s Law
In the circuit shown on the right side of the screen we know the value of the
battery (voltage) and the value of the current but we do not know the value of the
resistor. We can easily calculate the resistance by using Ohm's Law as shown.
Slide# 21
Ohm’s Law
As you have seen, the formulas of Ohm's Law can be used to calculate the values
of current, voltage, and resistance.
Ohm's Law is a basic but very useful law which is widely used from beginners to
engineers to calculate current, voltage and resistance.
In more complex circuits Ohm's Law is used in conjunction with other laws, but it
is still used.
Slide# 22
Ohm’s Law
Review
Electric current is the flow of electrons through a conductor. It is
measured in Amps. The letter “I” is used to represent current.
Voltage is the force or electric pressure that allows current flow.
It is measured in volts. The letter “V” (or sometimes “E”) is used
to represent voltage.
Resistance is the opposition to current flow. It is measured in
ohms (Ω). The letter “R” is used to represent resistance.
Current (I), voltage (V), and resistance (R) are the three
parameters found in every electronic circuit no matter how
simple or complex they are. Ohm's law establishes the
relationship between these three parameters.
Slide# 23
Ohm’s Law
Review
As the voltage applied to a circuit increases, the current that
flows through the circuit also increases, as shown in slides 8
through 10.
As we increase the resistance in a circuit, the current decreases,
as shown in slides 12 through 14.
Ohm's Law states that the current that flows in a circuit is
directly proportional to the voltage and inversely proportional to
the resistance.
Slide# 24
Ohm’s Law
Review
We can use the Ohm's Law formula to calculate
current, voltage and resistance.
Slide# 25
Ohm’s Law
Test
1. Electric current is measured in _____.
2. Voltage is measured in _____.
3. Resistance is measured in _____.
4. Current, voltage and resistance are three elements found in
every electronic circuit.
5. The current that flows through a circuit is directly
proportional to the _____ in the circuit.
Slide# 28
Ohm’s Law
Test
1. Electric current is measured in _____.
A. Amps
2. Voltage is measured in _____.
3. Resistance is measured in _____.
4. Current, voltage and resistance are three elements found in
every electronic circuit.
5. The current that flows through a circuit is directly
proportional to the _____ in the circuit.
Slide# 28
Ohm’s Law
Test
1. Electric current is measured in _____.
A. Amps
2. Voltage is measured in _____.
A. Volts
3. Resistance is measured in _____.
4. Current, voltage and resistance are three elements found in
every electronic circuit.
5. The current that flows through a circuit is directly
proportional to the _____ in the circuit.
Slide# 28
Ohm’s Law
Test
1. Electric current is measured in _____.
A. Amps
2. Voltage is measured in _____.
A. Volts
3. Resistance is measured in _____.
A. Ohms
4. Current, voltage and resistance are three elements found in
every electronic circuit.
5. The current that flows through a circuit is directly
proportional to the _____ in the circuit.
Slide# 28
Ohm’s Law
Test
1. Electric current is measured in _____.
A. Amps
2. Voltage is measured in _____.
A. Volts
3. Resistance is measured in _____.
A. Ohms
4. Current, voltage and resistance are three elements found in
every electronic circuit.
A. True
5. The current that flows through a circuit is directly
proportional to the _____ in the circuit.
Slide# 28
Ohm’s Law
Test
1. Electric current is measured in _____.
A. Amps
2. Voltage is measured in _____.
A. Volts
3. Resistance is measured in _____.
A. Ohms
4. Current, voltage and resistance are three elements found in
every electronic circuit.
A. True
5. The current that flows through a circuit is directly
proportional to the _____ in the circuit.
A. Voltage
Slide# 28
Ohm’s Law
Test
6. The current that flows through a circuit is inversely
proportional to the _____ in the circuit.
7. The basic formula of Ohm’s Law is _____.
8. What is the current in this circuit?
9. What is the voltage in this circuit?
10. What is the resistance in this circuit?
Slide# 28
Ohm’s Law
Test
6. The current that flows through a circuit is inversely
proportional to the _____ in the circuit.
A. Resistance
7. The basic formula of Ohm’s Law is _____.
8. What is the current in this circuit?
9. What is the voltage in this circuit?
10. What is the resistance in this circuit?
Slide# 28
Ohm’s Law
Test
6. The current that flows through a circuit is inversely
proportional to the _____ in the circuit.
A. Resistance
7. The basic formula of Ohm’s Law is _____.
A. I = V/R
8. What is the current in this circuit?
9. What is the voltage in this circuit?
10. What is the resistance in this circuit?
Slide# 28
Ohm’s Law
Test
6. The current that flows through a circuit is inversely
proportional to the _____ in the circuit.
A. Resistance
7. The basic formula of Ohm’s Law is _____.
A. I = V/R
8. What is the current in this circuit?
A. 2.4 Amps
9. What is the voltage in this circuit?
10. What is the resistance in this circuit?
Slide# 28
Ohm’s Law
Test
6. The current that flows through a circuit is inversely
proportional to the _____ in the circuit.
A. Resistance
7. The basic formula of Ohm’s Law is _____.
A. I = V/R
8. What is the current in this circuit?
A. 2.4 Amps
9. What is the voltage in this circuit?
A. 12 Volts
10. What is the resistance in this circuit?
Slide# 28
Ohm’s Law
Test
6. The current that flows through a circuit is inversely
proportional to the _____ in the circuit.
A. Resistance
7. The basic formula of Ohm’s Law is _____.
A. I = V/R
8. What is the current in this circuit?
A. 2.4 Amps
9. What is the voltage in this circuit?
A. 12 Volts
10. What is the resistance in this circuit?
A. 4.5Ω
Slide# 28